1. Field of the Invention
The present invention relates to a disk drive, and more particularly to a magnetic hard disk drive ("HDD") having a head stack assembly including an actuator arm having integral conductors rigidly affixed to the sides thereof and a head gimbal assembly attached to the actuator arm without a swage plate.
2. Description of the Prior Art and Related Information
A typical hard disk drive includes a head disk assembly ("HDA") and a printed circuit board assembly ("PCBA"). The HDA includes at least one magnetic disk ("disk"), a spindle motor for rotating the disk, and a head stack assembly ("HSA") that includes a head with at least one transducer for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly ("HGA") that extends from the actuator assembly and biases the head toward the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement.
A "rotary" or "swing-type" actuator assembly comprises a body portion that rotates on a pivot bearing cartridge between limited positions, a coil portion that extends from one side of the body portion to interact with one or more permanent magnets to form a voice coil motor, and an actuator arm that extends from an opposite side of the body portion to support the HGA.
A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a head attached to the gimbal. The load beam has a spring function that provides a "gram load" biasing force and a hinge function that permits the head to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a gimbal end that connects to the gimbal that carries the head and transmits the gram load biasing force to the head to "load" the head against the disk. A rapidly spinning disk develops a laminar air flow above its surface that lifts the head away from the disk in opposition to the gram load biasing force. The head is said to be "flying" over the disk when in this state.
Signals induced on the head, during read and write operations, must be carried to the proximal end of the HSA, where the flex cable assembly is attached. Typically, discrete conductors attached to the sides of the actuator arm are used. Such discrete conductors conventionally include conducting wires surrounded by insulating tubes. Electrically connecting these discrete conductors and attaching them to the sides of the HSA has traditionally been a painstaking manual process, which not only adds to the overall manufacturing cost of the HSA, but also increases the probability of introducing manufacturing defects therein, thereby decreasing the reliability of the resultant disk drive.
One prior art solution to the problems associated with the use of discrete conductors, as described above, is to use an actuator arm flex circuit which includes vertically spaced-art conductive traces for carrying signals to or from a head in a prior art disk drive. The arm flex circuit is supported on only one side surface of a corresponding actuator arm and extends along the length of the actuator arm such that conductive pads ("proximal conductive pads") positioned near a body portion of a head stack assembly mate, via solder bumps, with corresponding conductive pads ("main flex conductive pads") on a main flex circuit. The main flex circuit is positioned between the arm flex circuit and the body portion. The conductive traces include conductive pads ("distal conductive pads") which mate, via solder bumps, with corresponding conductive pads ("base region conductive pads") positioned on a load beam. The solder bumps serve to electrically connect the distal conductive pads and the base region conductive pads such that the head and electrical components on the main flex circuit are electrically interconnected. However, a swage plate is attached to the load beam such that the load beam is attached to the actuator arm by a swaging technique to be described below.
Conventionally, the HGA is attached to the actuator arm via a swage plate, also called a nut plate. A swage plate is a thin metallic plate including a circular bore that extends into a short cylinder. The cylinder of the swage plate is introduced through corresponding mating holes near the proximal end of the HGA and the distal end of the actuator arm; the swage plate, HGA and actuator arm thereby assuming a stacked configuration. Thereafter, a swage ball, also called a nut ball, is forced through the cylinder. As the diameter of the swage ball is slightly larger than the internal diameter of the cylinder of the swage plate, the inner walls of the cylinder expand somewhat forcing the outer walls of the cylinder to interfere with the corresponding mating hole in the actuator arm, thereby securing the swage plate, HGA and actuator arm together. However, securing the HGA to the actuator arm via a swage or nut plate adds additional weight to the HSA, which translates into greater inertia of the HSA and slower drive access times. Moreover, such a swaging technique is complex and requires several precise manufacturing steps, thus adding to the total cost of the HSA, one of the costliest elements of the disk drive to manufacture.